Corrosion-resistant cemented titanium



CIDE MATE Thomas Raine, Braall, Cheshire, England, assignor to American Electric Metal Corporation, Yonkers, N. Y a corporation of Maryland No Drawing. Application May 22, 1953, Serial No. 356,873

l 2 Claims. (Cl. 29-1825) The present invention relates to corrosion-resistant cemented titanium carbide material for use in applications such as gas turbine rotors or buckets, which require corrosion-resistance and strength at high temperatures within oxidizing temperatures, and the production of such material.

In the past, it was believed that in producing cemented titanium carbide material of high corrosion-resistance it was essential to combine at least 60% by weight of titanium carbide with a cementing alloy addition of nickel, cobalt and chromium. However, the best prior cemented titanium carbide material of this type exhibited a great degree of brittleness and could not be used in applications which required a material of substantial toughness at elevated temperatures.

The present invention is based on the discovery that a superior cemented titanium carbide material exhibiting a substantial degree of toughness at elevated temperatures is obtained by combining 40% to 55% and up to 60% of a carbide phase consisting principally of titanium carbide with a cementing addition consisting of at least 10% and up to 30% chromium, at least 4% and up to 25% cobalt and the balance nickel. (Unless otherwise specifically stated, all proportions are given herein by weight).

In the tough corrosion-resistant material of the invention, the titanium carbide may to advantage be combined wtih a small addition of molybdenum carbide which may form about .5 to 1% of the material. In some cases, the carbide phase may combine titanium carbide with up to about 50% by weight of light carbides of other metals having a high melting point such as carbides of vanadium, zirconium and/ or chromium.

There will now be described, by way of example, one method for producing tough cemented titanium carbide material of the invention which has proven satisfactory in commercial use.

In producing pure titanium carbide powder for cemented bodies of the invention, one may start with impure titanium carbide powder obtained by reacting titanium oxide TiOz with carbon, which powder contains approximately 18.2% carbon combined with titanium and approximately 0.6 free carbon. The impure titanium carbide is then mixed with 1% molybdenum oxide M003 together with graphite and 10% pure nickel powder. The mixture so prepared is then ball milled in dry state for about 20 hours. The ball milled mixture is then pressed or compacted into slugs, without any lubricant. The compacted slugs are heated at about 225 C. for about 35 minutes in a dry hydrogen atmosphere, whereupon the slugs are crushed and screened into 100 mesh powder. The fine powder so obtained is leached with HCl to remove free nickel and iron picked up in ball milling. After leaching, the resulting powder analyzes as consisting of substantially pure titanium carbide containing about /2 molybdenum carbide in solid solution and about 0.4% free carbon.

With the pure titanium carbide powder so obtained,- a

2,736,086 Patented Feb. 28, 1956 desired cemented titanium carbide body of the invention may be produced by the following procedure. 50% of the pure titanium carbide powder is mixed with a cementing metal either in pure or alloyed form containing 15% chromium, 8% cobalt, 27% nickel. The mixture of the titanium carbide powder and the metal powder is ball milled in acetone for 7 days in a stainless steel mill. The ball milled powder mixture is then dried, screened and mixed with a camphor-ether solution for approximately 1 hour, and the ether is thereafter evaporated.

The so-treated powder mixture is then powdered into a powder body about mesh particle size. The soobtained powder is then pressed or compacted in a die with the pressure raised to about 5 t. s. i. (tons per square inch). After removing from the die, the compact is presintered at about 900 C. in vacuum. The duration of the presintering depends on the size of the compact. Thus, in the case of a large compact such as 6 inches diameter and 4 inches height, the sintering temperature is reached Within about 4 hours and the compact is thereafter maintained at the sintering temperature of about 900 C. for about 20 minutes. Thereafter, the compact is cooled in a hydrogen atmosphere.

The presintered compact so obtained is then machined to give it the desired final shape allowing approximately 50% for shrinkage during the final sintering. In the final sintering, the shaped sintered compact is heated in a vacuum within a furnace to a temperature between about 1000 to 1200 C. and below about 1300 C. and maintained at such elevated temperature for approximately 2 hours to permit removal of oxides from the body. Thereafter, the temperature of the furnace is raised to bring the body to about l400 to 1450 C. followed by cooling in vacuum. The body so obtained has a modulus of rupture between about 150,000 to 200,000 p. s. i. (pounds per square inch) and about 81 to 88 Rockwell A hardness. It has a stress-to-rupture life at 14,000 p. s. i. of 100 hours at 950 C. and good oxidation resistance at temperatures up to about 950 C.

Similar desirable materials may be produced with other proportions of the ingredients of the ranges given above such as 40% titanium carbide, 12% chromium, 12% cobalt and 36% nickel.

The features and principles underlying the invention described above in connection with specific exemplifications will suggest to those skilled in the art many other modifications thereof. It is accordingly desired that the appended claims shall not be limited to any specific features or details shown and described in connection with the exemplifications thereof.

I claim:

1. A shaped body of high hot strength and resistance to corrosion in oxidizing gases at high temperatures, 40% to 60% of said body consisting principally of titanium carbide, the balance of said body consisting of at least 10% and up to 30% chromium, 4% to 5% cobalt and as balance nickel, said body having been shaped after presintering at a temperature below about 1300 C. and further sintered at an elevated temperature above about 1300 C.

2. A shaped body as claimed in claim 1, wherein the titanium carbide contains up to about 1% of molybdenum carbide in solid solution.

References Cited in the file of this patent UNITED STATES PATENTS 1,728,909 Schroter Sept. 17, 1929 1,992,372 Holzberger Feb. 26, 1935 2,162,574 Dawihl June 13, 1939 2,170,432 Schwarzkopf Aug. 22, 1939 

1. A SHAPED BODY OF HIGH HOT STRENGTH AND RESISTANCE TO CORROSION IN OXIDIZING GASES AT HIGH TEMPERATURES, 40% TO 60% OF SAID BODY CONSISTING PRINCIPALLY OF TITANIUM CARBIDE, THE BALANCE OF SAID BODY CONSISTING OF AT LEAST 10% AND UP TO 30% CHROMIUM, 4% TO 5% COBALT AND AS BALANCE NICKEL, SAID BODY HAVING BEEN SHAPED AFTER PRESINTERING AT A TEMPERATURE BELOW ABOUT 1300* C. AND FURTHER SINTERED AT AN ELEVATED TEMPERATURE ABOVE ABOUT 1300* C. 